1. Field of the Disclosure
The present disclosure relates to a push switch equipped with a capacitance sensor having a function capable of detecting a touch on an operation surface by a human body (finger) and an input device including a plurality of the capacitance-sensor-equipped push switches arranged in parallel.
2. Description of the Related Art
Easy-to-operate push switches are often arranged in operating areas of vehicle-mounted controllers of, for example, air conditioners, audio systems, and navigation systems. In an operating area of this type, a plurality of push switches are typically arranged in parallel to each other. A user therefore has to visually confirm the position of a desired push switch and then push the switch. However, while driving, the user has to take his or her eyes off forward roadway and look at hand in order to find a desired push switch and put a finger on the switch. Disadvantageously, the user may tend to neglect to pay attention to the roadway.
There has been proposed a push switch equipped with a capacitance sensor function for detecting, on the basis of a change in capacitance caused when an operation surface is touched by a human body, whether a user's finger is in contact with the operation surface (refer to Japanese Unexamined Patent Application Publication No. 2007-73506, for example). In the related-art push switch equipped with the capacitance sensor, a detecting electrode made of a metal plate is integrated with the rear surface of an operation surface of an operating member. When a user's finger touches the operation surface, a detection signal indicative of a change in capacitance is supplied from the detecting electrode through a wiring substrate to a control unit. The operating member is supported by a support such that the operating member is movable downward and upward in the direction (hereinafter, “pushing direction”) in which the operating member is pushed. When the user pushes the operating member, a movable contact moved by the operating member is come into contact with a fixed contact, so that a switch-on signal indicating the electrical connection of the contacts is supplied through the wiring substrate to the control unit. In the related-art push switch, the detecting electrode is moved down or up integrally with the operating member. Accordingly, one end of an electrically conductive coil spring is brought into resilient contact with the wiring substrate with a wiring pattern or the like and the other end of the coil spring is brought into resilient contact with the detecting electrode so that the electrical connection between the detecting electrode and the wiring substrate is kept even when the operating member is moved down and up.
When the capacitance-sensor-equipped push switches schematically constructed as described above are used as operating switches of a vehicle-mounted controller, a display, often installed in a position where a user can see the display while hardly taking user's eyes off forward roadway, can be allowed to display information so that the user can immediately know which push switch is being touched by a user's finger. Consequently, the user can correctly select a desired push switch to perform a pushing operation without looking at hand. Advantageously, the user can easily operate the vehicle-mounted controller without neglecting to pay attention to forward roadway, thus remarkably increasing safety and operability.
In some cases, it is difficult to design an input device including a plurality of push switches parallel-arranged in an operating area so that operation surfaces of the switches are arranged at the same height (or level) relative to a wiring substrate. For example, since there are many design and space restrictions on an operating area of a vehicle-mounted controller, the operation surfaces of the parallel-arranged push switches have to be placed at different heights relative to the wiring substrate in many cases. In such a case, assuming that the parallel-arranged push switches each have a capacitance sensor function, if the shapes of operating members of the push switches are made different from each other, it is difficult to arrange the operation surfaces of the push switches at different heights relative to the wiring substrate. Previously, therefore, the length in the extending and retracting direction (pushing direction) of a coil spring interposed between a detecting electrode and the wiring substrate varies from switch to switch.
FIG. 9 illustrates a case where two push switches 20 are arranged in parallel on a wiring substrate 30, an operating member 21 of each push switch 20 is mounted on urging member 25 and is supported by a support 26 so that the push switch 20 is movable down and up in FIG. 9 and the levels of operation surfaces 21a of the push switches 20 are made different from each other. In this case, coil springs 22 of the left push switch 20 whose operation surface 21a is at a lower level are incorporated in the switch such that the coil springs 22 are more compressed than the other coil springs 22 of the right push switch 20. The rear surface of the operation surface 21a of the operating member 21 of each push switch 20 is fixed to a detecting electrode 23. The distance between the detecting electrode 23 and the wiring substrate 30 in the left push switch 20 is shorter than that in the right push switch 20, because the coil springs 22 of the push switch 20 differ in length in the extending/retracting direction from those of the other push switch 20 in a non-operation mode. The detecting electrodes 23 are kept to be electrically connected to the wiring substrate 30 at any time, thus ensuring the capacitance sensor functions. In FIG. 9, a holding member 24 is fixed to each operating member 21 such that the holding member 24 is placed inside the operating member 21. Since the coil springs 22 are inserted through through-holes 24a of each holding member 24, the extending/retracting direction of the coil springs 22 can be made identical to the pushing direction, thus ensuring the reliability of electrical connection.
In the case where the coil springs 22 having the same length and spring constant are incorporated in the push switches such that the coil springs have different compressed states in order to make the levels of the operation surfaces 21a of the parallel-arranged push switches 20 different from each other, however, a reaction force caused by the coil springs 22 when the user pushes the operation surface 21a of the push switch 20 differs from push switch 20 to push switch 20. Disadvantageously, a pushing force varies from push switch 20 to push switch 20. To prevent a variation in pushing force, various coil springs 22 having different lengths and spring constants may be prepared. However, it is not preferable because the cost of parts of the push switches 20 is remarkably increased. If the push switches 20 are set so as to have a uniform distance between the detecting electrode 23 and the wiring substrate 30 irrespective of the level of the operation surface 21a, it is unnecessary to prepare various coil springs 22. However, it is undesirable because the distance between the operation surface 21a and the detecting electrode 23 differs from push switch 20 to push switch 20 and this results in a large variation in the accuracy of capacitance detection.